1. Field of the Invention
This invention relates to an electrostatic chucking device such as a device for producing an semiconductor integrated circuit which can fix and hold an electrically conductive substance such as a wafer on a prescribed portion of a processor in vacuum, and a process for producing the same, and particularly to an electrostatic chucking device having improved heat conductivity (heat radiation ability or temperature regulating ability) and improved adhesion by suction.
2. Description of Related Art
In the stage for processing a semiconductor wafer, it is required to fix and hold the semiconductor wafer on a prescribed portion of a processor. In particular, in the manufacture of an integrated circuit in which fine patterns are drawn on the semiconductor wafer to form a lot of semiconductor elements, it is necessary to ensure the holding of the semiconductor wafer on a flat face.
In conventional, as means for holding the semiconductor wafer, a chucking device in a mechanical, vacuum (utilizing the difference between fluids) or electric manner has been utilized. Of these, the chucking device in an electric manner, i.e., an electrostatic chucking device, has the merits that even in the case of an uneven semiconductor wafer, it can be fixed in a close manner, the device can easily be handled and easily be used even in vacuum, etc.
When beam particles, etc. are injected and impacted during the processing of the semiconductor wafer, heat energy is generated on the semiconductor wafer. In the case where the heat energy cannot easily be discharged, the local swelling and deformation of the semiconductor wafer will be caused. Consequently, it is necessary that the heat generated during the processing is escaped to the side of the metal base to make temperature distribution on the semiconductor wafer uniform. For this reason, it is desired for the electrostatic chucking device utilizing in these applications to have functions of holding the semiconductor wafer on a prescribed portion without failing and at the same time of having high heat conductivity.
One embodiment of the conventional electrostatic chucking device, for example, as disclosed in Japanese Patent Publication 87177/93, will be described by referring to the drawing. FIG. 4 is a schematic cross-sectional view showing one embodiment of the conventional electrostatic chucking device. A metal base 1 is made up of a highly heat conductive metal such as copper and aluminium. On the metal base 1, in order to regulate the temperature by passing isothermic water, etc., spaces 6 for regulating temperature are provided. While an electrode layer 3a is provided on an upper portion of the metal base 1 so as to have a function of electric chucking, an insulating plastic film 4b is provided between the electrode layer and the metal base in order to avoid any electric shortage among the electrode layer, the metal base and external portions. On the upper portion of the electrode layer 3 provided on the insulating plastic film 4b, a plastic film 4a is provided so as to cause a semiconductor wafer 5 to exhibit adhesion by suction and to protect the metal base 1.
In the above-mentioned electrostatic chucking device, as the electrode material for the electrode layer 3a, a copper foil having a thickness of 1/2oz (approximately 18 microns) or 1 oz (approximately 35 microns) is generally used, and as the insulating plastic films 4a and 4b, films having a thickness of approximately 50 microns such as made of polyimide or Teflon are used considering electric characteristics and heat resistance. They are laminated each other via adhesive layers having a thickness of from 10 microns to 50 microns (2a, 2b, 2c).
In the conventional electrostatic chucking device, since the plastic films 4a and 4b are interposed between the semiconductor wafer 5 and the metal base 1 in order to secure mutual electric insulation between the semiconductor wafer 5, the electrode layer 3a and the metal base 1, the function of regulating temperature is poor due to the low heat conductivity thereof. In other words, there poses a problem that a cooling function of the circuit base to the semiconductor wafer is insufficiently acted.
Since a metal foil having a thickness of approximately from 18 to 35 microns is used as the electrode layer, uneveness in approximately the same degree as thickness of the metal foil used as the electric layer occurs between the portion where the electrode exists and the portion where no electrode is existent on the wafer-provided face (suction face) of the electrostatic chucking device. Consequently, there is a problem that the heat conductivity in vacuum becomes locally poor when the semiconductor wafer is fixed by suction, because the semiconductor wafer is separated at the cavity portion. This phenomenon is significant at the outer circumference where no cooling gas is used, and the portion of the width of insulation is co-called in a floated state, causing the problem that the heat conductivity in vacuum becomes poor.
Moreover, an adhesive is used for laminating these materials. However, when being corrugated, since there are large cavities at these bump portions, which is difficult to be filled up by an adhesive and, thus, fine cavities are formed along the bump, the width of insulation against the outer circumference should be widened in relation to dielectric strength. This causes the problem that the adsorption area becomes narrow.
FIG. 5 explains the above state in the conventional electrostatic chucking device, and shows the state that the uneveness is formed on the wafer-provided face of the plastic film, spaces 7 are formed when providing the semiconductor wafer, and cavities 8 are formed along the bump. The other symbols in FIG. 5 are the same as those described above.